1. Field of the Invention
This invention relates to mobile radio signal diversity, and more particularly, to encoding downlink and uplink mobile radio data transmitted in multiple timeslots within a frame from a single source, wherein portions of the data are encoded with different spreading sequences.
2. Description of the Prior Art
Data is transmitted in CDMA radio systems by means of sending a code sequence for each bit or data symbol. Each user is assigned a different code. If a user transmits data on multiple channels, each user channel is assigned a different code. By using different codes, multiple users may transmit signals within the same frequency band within the same timeslot. The codes are generally designed such that they have good cross-correlation properties. Good cross-correlation properties allow a receiver to correlate a received composite signal containing a number of codes in order to separate out one or more individually coded signals from the composite signal.
Good cross-correlation properties cannot always be obtained among a group of selected codes. Furthermore, multipath in a radio channel can change the cross-correlation properties of a signal before a signal arrives at a receiver. Therefore, there are some instances where the cross-correlation among signals is good, and other instances when the cross correlation deteriorates. Poor cross correlation may lead to inadequate radio link performance, an increase in bursts of data errors, and loss of the spectral efficiency of the system.